The F-35 Lightning II is the most expensive fighter jet in military history, with a total cost of nearly $400 billion to produce a planned fleet of more than 2,400 planes. Just don't expect any of them to fly with anything warmer than tepid jet fuel.

When the fuel for the F-35 hits higher temperatures, there's a chance the jets will experience what the Air Force described as a "shutdown." To keep each $100 million-plus jet running at Luke Air Force Base, located northwest of Phoenix, the 56th Logistics Readiness Squadron is preparing to repaint its fuel trucks, currently green.

"We are taking proactive measures to mitigate any possible aircraft shutdowns due to high fuel temperatures in the future," Chief Master Sergeant Ralph Resch explained last week in an Air Force statement. His team of fueling specialists got the idea to paint the trucks from Edwards Air Force Base in the Mojave Desert, where summer temperatures routinely hit 110 degrees. A coat of white paint, which better reflects heats, could help cool down the fuel.

The Air Force insists that the F-35 has performed well during test flights in hot desert climates. Still, the warm-fuel glitch would hardly be the first unforeseen issue to hamper the F-35 program, whose long litany of development woes ranges from engine fires and oil leaks to enormous cost overruns.

Replacing the green paint job with a white-colored solar polyurethane enamel, even if it helps the fussy F-35s, will create new headaches for the Air Force. Refueling units often serve in combat zones, and a big white fuel truck is a fine target—sticking out "like a sore thumb down range," as the Air Force put it. The fueling specialists at the Arizona air base are going to test a new shade of green paint, along with white, to see if the less-conspicuous color can also help keep lower the fuel's temperature. Future plans for the F-35 include the construction of parking shades to shield the fuel trucks from direct sunlight.

Major Matt Hasson, a spokesman for Luke Air Force Base, describes the truck repainting as "a local mitigation effort that has nothing to do with the F-35 fleet Air Force-wide." He said the 14 F-35s at Luke have performed "outstanding" flights during the Arizona summer. "In the Air Force," Hasson adds, "you lean forward" and address potential problems such as hot weather. Michael Rein, a spokesman for Lockheed Martin, the F-35s' primary contractor, acknowledged a temperature limit for jet fuel, but neither he nor Hasson could say just how warm things can get before problems arise. "The F-35 does not have any fuel thermal limitations that should require any modifications to operational sites' fuel trucks," Rein said in an e-mail.

U.S. Air Force via Bloomberg

If you are curious why a gleaming new fighter jet—for which U.S. taxpayers paid top dollar—should be so delicate about its fuel, you are not alone. "Is our next conflict in Siberia?" snarked a commenter on the Air Force's website. "I hope we won't have to fight any wars where the temperature goes up and where there's a lot of sunlight, say, in the Middle East, for example," added another. The military blog Foxtrot Alpha described the F-35's fuel system as a "giant heat sink" that helps to dissipate the heat loads generated by the plane's avionics systems and engine.

Last week the House of Representatives approved a $577 billion defense bill for the current 2015 fiscal year, agreeing to the Pentagon's full funding request for the F-35. Lockheed Martin and Pratt & Whitney, the engine supplier, have been working to reduce the unit costs of the program, which has been criticized for years for its outsized impact on U.S. defense budgets. Over the next five decades, the military says the fleet will cost around $1 trillion to operate and maintain.

It won't take a combat situation to make too-warm jet fuel a potential problem. Earlier this year, the 61st Fighter Squadron at Luke received the first of what is expected to become 144 F-35s in coming years. The Arizona base will serve as one of three U.S. training locations for pilots of the F-35, which is expected to enter service next summer with the Marine Corps before joining the Air Force arsenal a year later.

The F-35 comes in three variants for the Air Force, Navy, and Marine Corps, giving it the moniker of Joint Strike Fighter. The Pentagon says the plane will serve as the backbone of U.S. air combat capabilities into the 2060s. The aircraft is designed to replace the F-16 Falcon and A-10 Thunderbolt "Warthog" fighters, both of which are seeing duty as part of the current U.S. campaign against Islamic State militants.

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